Device for fabricating pump impellers



Feb. 9, 1943. w. H. CURTIS DEVICE FOR FABRICAIING PUMP IMPELLERS FiledAug. 17, 1940 Patented Feb. 9, 1943 DEVICE FOR FABRIGATING PUMPIMPEILERS William E. Curtis, Dayton, Ohio, assignor to Curtis PumpCompany, Dayton, Ohio, a corporation of Ohio Application August 17,.1940, Serial No. 353,015

1 Claim.

This invention relates to a device for fabricating pump impellers, moreparticularly small impellers for centrifugal and similar pumps.

It has heretofore been the practice to fabricate centrifugal pumpimpellers by casting them of metal in sand molds, such as are used incommercial foundries. The castings thus obtained cannot ordinarily be ofsuch proportions as to be best suited for the duties that the impelleris intended to perform, Owing to the inherent limitations in sand moldcastings. As the overall dirnensions of pump impellers becam smallerduring recent years, it was found to be impossible to cast suitablemetal in suificiently thin sections to permit the attainment of maximumelliciency in the operation of the impeller as an element of thecompleted pump. Consequently, a great deal of machine or hand labor wasnecessarily expended upon the casting before it could be satisfactorilyemployed for its intended duty.

It is also obvious that, in the production of small impellers by castingmethods, the choice of material is necessarily limited to those metalsor alloys that can be cast. For this reason, it often became necessaryto use a metal or alloy that was not best suited to withstand theconditions to which the pump impeller would be subjected in service.

In accordance with my present invention, the vanes and impeller body areseparately formed and then assembled by a brazing or similar operation.In this way, the vanes can be formed from the desired metal or alloy, asfor instance a highly heat resistant steel, by a rolling or drawingoperation, or by ordinary punch press procedure, while the impeller bodyportion may be produced either from a forging or from solid bar stock,using the same or a different metal or alloy composition. My inventionthus avoids the disadvantages of casting operations heretofore used inthe making of pump impellers.

It is therefore an important object of this invention to provide adevice for fabricating pump impellers that 'will obviate thedisadvantages heretofore attendant upon the use of casting methods, andat the same time to provide a method of fabricating pump impellers thatwillpermit the use of more suitable metals and alloys in theconstruction of the impeller.

It is a further important object of this invention to provide a devicefor fabricating pump impellers that lends itself to large scaleproduction and that eliminates to a considerable extent the amount ofmachine and hand labor previously required in machining cast impellersto the final form and dimensions required for their efficient operation.

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and the accompanying drawinThis invention (in a preferred form) is illustrated in the drawing andhereinafter more fully described.

On the drawing:

Figure l is a top plan view of the upper cap member of a two-part jig,illustrating the manner of holding th individual impeller vanes in placeon the face thereof by means of locating pins.

Figure 2 is a longitudinal sectional view taken along the line IIII ofFigure 1 with the cap member in its temporary position for the mountingthereon of the vanes and the positioning over the top of the vanes of abrazing shim or the like.

Figure 3 is a longitudinal sectional view of an assembled jig with theimpeller body portion, brazing shim and impeller vanes positioned inplace therein.

Figure 4 is a partly diagrammatic view showing a mufile, furnace or thelike, with the impeller parts assembled within the jig and positionedwithin the furnace for the brazing operation.

Figure 5 is a top plan view of a completely fabricated impeller with thevanes brazed in position on the impeller body.

The reference numeral I0 indicates the top part, or cap member, of atwo-part jig. Said cap member ID is preferably in'the form of a cylinderhaving a diameter approximately equal to the outside diameter of thevanes that are to be assembled thereon. The material of which the cap I0is formed is not important so long as it is capable of withstanding thetemperatures to which it is subjected during the brazing operationwithout appreciable distortion, and without fusing or becomingunited tothe vanes that are in contact therewith during such brazing the vanes l3that are to be temporarily held against displacement and distortion bymeans of said pins ll. As shown, there are four locating pins I I foreach one of the vanes I3, two of the pins being arranged to bear againstone side of a vane and the other two pins to bear against the oppositeside of the vane, when the vane is positioned on edge between itsparticular set of locating pins. The spacing and location of the pins IImust be so accurately accomplished that the vanes I3 can be slipped intoposition without being sprung out of their original state of curvatureand yet be firmly braced after insertion in place so that no distortionor displacement of the vanes will occur during the relatively hightemperature brazing operation.

The vanes themselves may be conventional in their form and design, ormay be of the particular design that is described and claimed in thecopending application of Russell R. Curtis entitled Booster pump foraircraft fuel system, Serial No. 352,064, filed August 10, 1940. Inaccordance with the invention described in that application, the vanesI3 are formed of relatively thin metal as spiral segments, and aretapered along one edge, as at I4, from approximately their mid portionsto their inner ends I5. Each valve I3 is thus formed with one plane edgeI6 (Fig. 1) continuous throughout the'entire length of the vane, andwith a shorter plane edge I'I (Fig. parallel thereto.

In assembling the vanes I3 upon the cap member III, the cap member I0 istemporarily positioned with the plane face I2 uppermost and the vanes I3are inserted with their shorter edges I1 the bolt 3|. Various brazingmaterials may be employed, such as copper, copper-containing alloys orbrass, and the so-called silver solders, such as alloys of silver, zincand copper. Preferably, a silver solder is used that is relatively highin zinc and low in silver, and which melts at approximately 1250 F.Since all silver alloys, in general, require the use of a. special flux,when the brazing shim 34 is formed of.a silver alloy, a suitable flux iscoated thereover. In the case of brass, a flux is also desirable,although with a pure copper shim, the flux may be omitted entirely.Suitable compositions of flux for the various brazing materials are wellknown to those skilled in this art.

With the cap member I0 and assembled vanes I3 in the position shown inFigures 1 and 2, and with the shim 34 in place, the base 20 is invertedand superposed above the cap member ID so as to rest upon the shim 34.The bolt 3| is then inserted in place and the nut 33 threaded home tohold the impeller body 25 and vanes I3 in their proper relationship,except for the intervention of the shim 34. After the complete assemblyhas been firmly closed by means of the bolt 3| and nut 33, the assemblyis then inverted to its normal position (Figs. 3 .and 4) with the basememin contact with said plane surface I2, as illustrated in Figure 1. Asthere shown, the inner ends of the vanes I3 lie on a circle concentricwith the axis A of the cap member ID, and with their outer ends I8 lyingin a circle substantially coincidental with the circle of the peripheryof the cap member itself. Said cap member I0 is provided with a bore I9extending therethrough. The other part of the jig comprises a basemember 20, which may also be formed of high chrome steel or othersuitable metal and which is provided with a bore 2| of the sam diameteras that of the bore I9 but countersunk at both ends, as at 22 and 23.The countersunk portion 23 is of such length and diameter as to permitthe insertion thereinto of the hub 24 of an impeller body part 25. Theimpeller body part 25 comprises a disk-shaped flange 26 having a planeface 21 and an opposite tapered face 28, centrally of which is formedthe integral hub 24. When positioned on the base 20, the impeller 25automatically seats itself, with the hub 24 extending into thecountersunk bore portion 23 and with the tapered face 28 in full surfacecontact with a similarly tapered upper face 29 of said base 20.

The other countersunk bore portion 22 is for the reception of the head30 of a bolt 3| which freely extends through said bores 2| and III ofthe base 20 and cap I0, respectively, and also through the hub 24 of theimpeller 25. Said bolt 3| is provided with a threaded end 32, upon whicha nut 33 is adapted to be threaded to hold the base 20, cap I0, andassembled impeller parts in their proper relation, as illustrated inFigure 3.

After the vanes I3 have been assembled upon the face I2 of the capmember I0, as previously described, and while the cap member is still inthe position illustrated in Figures 1 and 2, a brazing shim 34 is laidover the then uppermost vane edges I6. The brazing shim 34 may be formedof any suitable brazing material and is preferably in the shape of acircular washer having a central opening 35 to permit the passagetherethrough of her 20 at the bottom and the cap member ID thereabove.In this position, the assembly is placed within a muffle, or furnace 36,which may be suitably heated by electrical or other means (not shown).The furnace 36 is then brought to a suitable brazin temperature, whichmay in general be between 1000 and 2000 F., but is preferably in theneighborhood of 1200 to 1550" F. The brazing is carried out in areducing atmosphere, preferably an atmosphere of hydrogen gas, or amixture of hydrogen and other non-oxidizing or reducing gases, such ascarbon monoxide, carbon dioxide and the like. The purpose of using areducing atmosphere, as is well known to those skilled in the art, is toprevent oxidation of the surfaces that are to be united and also tocause the copper, brass, silver solder or other brazing material tothoroughly and completely wet the surfaces that are to be bondedtogether. Under such conditions, the brazing material flows by capillaryaction into th joints that are to be united.

As the temperature is raised in the furnace 36, the material of thebrazing shim 34 fuses and flows over the contiguous surfaces of theimpeller vanes I3 and of the impeller body 25. The weight of the capmember II) is such as to force the vanes I3 downwardly into closeedgewise contact with the surface I2 of the impeller body 25, displacingthe excess of brazing material as the same melts or fuses between suchsurfaces. This insures the proper bonding of the vane edge surfaces I6with the plane surface I2 of the impeller body 25. The pins II are, ofcourse, sufficiently short as not to interfere with the pressureexerting function of the cap member I0 during the brazing operation.Also, as previously explained, the shank of the bolt 3| extends looselythrough the bore III of the cap member. In and serves merely as a guidefor said cap member while the same exerts its weight due to gravity uponthe assembled impeller parts.

During the brazing operation, if the vanes I3 were not laterally bracedas they are by means of the locating pins II, they would undoubtedlybecome distorted and displaced due to expansion at the high temperaturesof the brazing operation. It has been found, however, using the jig andmethod just described, that practically no displacement or distortion ofthe vanes l3 occurs during the brazing operation and that very littlemachining is necessary after the assembled impeller parts have beenremoved from the jig. The assembly may be either cooled within thefurnace 36, or, preferably, is removed from the furnace and cooled inthe air. Thereafter, the nut 33 is threaded off and the jigdisassembled. Practically the only machining that is necessary is thatrequiredto remove any excess of the brazing material and to bring theoverall dimensions of the now completely assembled impeller to therequired proportions. It is thus possible to fabricate a centrifugalpump impeller of the desired materials without sacrifice of operatingefliciency by reason of any departure from correct proportions for therespective elements. The fabricated impeller can consequently beobtained at reasonable cost by methods that may be used where high ratesof production are imperative.

While the foregoing constitutes the preferred embodiment of myinvention, it will be understood that the details thereof can be variedconsiderably. For instance, instead of using a shim or washer of brazingmaterial, as described, it is entirely feasible to provide the surfaceI! of the impeller body 25 with an electrodeposit of suitable brazingmaterial, such as copper, brass or the like, or to apply a powder, pasteor paint containing the brazing material, with or without a flux, oversaid surface l2 or over the surfaces of the vanes i3. comparativelylittle brazing material by weight is required, owing to the fact thatwhen fused in a hydrogen or other reducing atmosphere, the brazingmaterial will flow readily and, due to the capillary nature ofrelatively tight joints, will preferentially seek out such joints andflow into them. Thus the brazing material automatically flows to thepoints where it is actually needed for effecting the bonding of theparts to be united.

The weight of the cap member I may be selected in accordance with therequirements found by actual practice to give a satisfactory bondbetween the vanes l3 and the surface I! of the impeller body 25.Auxiliary pressure exerting means, such as a coiled spring positionedbetween the nut 33 and the upper surface of the cap member I0, might beused, if desired. a

It will, of course, be understood that various details of constructionmay be varied through a wide range without departing from the principlesof this invention and it is, therefore, not the purpose to limit thepatent granted hereon otherwise than necessitated by the scope of theappended claim.

I claim as my invention:

A device for insertion in a furnace to hold members to be brazed incooperable relation to each other and to automatically move said membersinto intimate relation during brazing in the furnace, said devicecomprising a base adapted to guidingly receive and support an impellerbody seated thereon, a weighted jig member disposed above said base andhaving spaced-apart means on its lower face adapted to guidingly receiveimpeller vanes disposed therebetween, shaft means on said base memberand extending thereabove and guidingly entered in said jig member, saidjig member and the vanes held thereby being normally spaced from saidbase by a normally rigid brazing shim interposed between an opposed edgeof said vanes and said impeller body, means on said shaft and engagingsaid jig member to fixedly retain the jig member, the

vanes, the shim, the impeller body, and the base in assembled relationfor initial insertion of the assembly in a furnace, and means comprisingsaid weighted jig member-movable to move opposed edges of the vanes intointimate contact with the impeller body as the shim melts under theinfluence of the heat of the furnace.

WILLIAM H. CURTIS.

